This invention relates to apparatus for extracting heat from articles, as in the freezing of foods, by directly contacting the articles with a liquid freezant, such as polyfluorinated saturated halohydrocarbon freezant, within an open topped vessel. More particularly, this invention relates to an open topped vessel hereinafter referred to as an initial quick freeze (IQF) pan in which the articles are initially contacted with liquid freezant.
Previous IQF pans, such as that disclosed in U.S. Pat. No. 3,479,833 issued to V. H. Waldin, typically include an upstream weir flow stabilizer of reverse curvature or "ski slope" configuration for inducing a current along the surface of a pool of liquid freezant therein for sweeping food particles dumped into the pool over a smooth crested downstream weir. The surface current is produced as freezant flowing off the end of the upstream weir drops into the pool. As falling freezant enters this pool, it stirs or agitates portions thereof into small eddies which entrain the remainder of the freezant within the pool and cause it to form a generally circular back-flow, the upper or surface layer of which is directed toward the downstream weir to provide or contribute to the above-described surface current.
To prevent frozen food particles from sticking to each other or to the pan surfaces, especially the bottom of the pan and the crest of the downstream weir, it is desirable to provide a uniform, high velocity surface current; however, the surface current which can be produced by backflow induced by the upstream weir in these prior IQF pans is of limited velocity. Slit openings, nozzles, jets, etc. have been proposed to supplement the effects backflow in order to increase the velocity of the surface current; however, the added surface flow produced thereby causes more freezant to be forced out of the IQF pan over the downstream weir without recirculation within the pan. Without significant freezant recirculation within the IQF pan, collection and evaporation losses of freezant once it leaves the pan, energy losses due to eddying within the freezant pool, and the additional energy required to pump in additional freezant to replace that lost over the downstream weir reduce the efficiency of the apparatus while raising its operating cost.